A pentamethylcyclopentadienylrhodium(III)‐catalyzed regioselective synthesis of indole‐2‐carboxamides is described employing N‐pyrimidylindoles and isocyanates as coupling partners via C H functionalization. A wide variety of indole‐2‐carboxamides can be synthesized via this method under relatively mild conditions with broad functional group tolerance. The effect of various directing group on this transformation was also studied, unveiling the pyrimidyl group as an easily installable and removable directing group.
A palladium(II)/copper oxide (Cu2O)‐catalyzed one‐pot decarboxylative and direct C H arylation of 2‐picolinic acid with aryl bromides has been developed. Various aryl bromides have been shown to be efficient coupling partners in the presence of dimethyl sulfate, furnishing symmetrical 2,6‐diarylpyridines in moderate to good yields.
An efficient dehydrogenative Diels–Alder (DHDA) reaction of prenyl derivatives with 2,3‐dichloro‐5,6‐dicyanobenzoquinone (DDQ) has been developed under mild conditions, leading to a series of cyclohexene derivatives with good to excellent yields and excellent diastereoselectivity.
A novel synthetic method to access fused indolin‐3‐ones with a tetrasubstituted carbon stereocenter has been developed via NHC‐catalyzed umpolung formal [3+3] cycloaddtion of enals with isatogens. This methodology could be also applied for the quick construction of the 6‐5‐5 tricyclic pyrrolo[1,2‐a]indole skeleton which is frequently found as a core structure of many indole alkaloids.
A three‐component reaction involving isocyanides, o‐alkynyltrifluoroacetanilides, and amines for the efficient synthesis of 2‐substituted 1H‐indole‐3‐carboxamidines has been developed. The reaction proceeds through intramolecular aminopalladation of alkynes activated by isocyanide‐ligated palladium(II) species. Dioxygen acts as the sole oxidant to regenerate the active palladium(II) species.
An efficient regioselective synthesis of 2‐acylpyrroles via palladium‐catalyzed addition of pyrroles with benzonitriles and subsequent hydrolysis is developed. The direct acylation reaction of protected as well as (NH)‐free pyrroles proceeded smoothly to afford 2‐acylpyrrole scaffolds of high biological interest.
A new transition metal‐free oxidative coupling of unactivated terminal alkenes with aldehydes and hydroperoxides in the presence of 10 mol% potassium tert‐butanolate (t‐BuOK) is described thereby realizing trifunctionalization of alkenes toward 2,3‐epoxy ketones. This method is applicable to a wide range of aldehydes, including aryl and alkyl aldehydes, with excellent functional group tolerance, and provides for the one‐step assembly of 2,3‐epoxy ketones.
3‐Substituted‐2H‐1,4‐benzoxazines undergo a highly enantioselective direct Mannich reaction with acetone in the presence of an L ‐proline catalyst at room temperature. The corresponding N‐heterocycles with α‐tetrasubstituted carbon stereocenters were obtained in good yields (48–92%) and excellent enantioselectivity (up to >99% ee). Furthermore, a novel modification involving the diastereoselective reduction of the Mannich adduct was carried out leading to the formation of a 1,3‐amino alcohol with a chiral tetrasubstituted carbon stereocenter in high yield.
In the presence of sodium carbonate, the [4+3] cycloadditions of α‐halogeno hydrazones with nitrones were performed efficiently, and affording 2,3,4,7‐tetrahydro‐1,2,4,5‐oxatriazepines in moderate to high yields.
Under zinc Lewis acid catalysis, terminal alkynes coupled dehydrogenatively with 1,8‐naphthalenediaminatoborane [HB(dan)]. It is important to note that the resulting alkynylboranes with an C(sp) B(dan) bond are isolable by column chromatography on silica gel (SiO2) and are usable as coupling partners for palladium‐ and copper‐catalyzed cross‐coupling reactions with (hetero)aryl halides.
A general method to generate umpolung of aldimines with cyanide was developed via the addition of cyanide to aldimines followed by a proton transfer from the carbon atom to the nitrogen atom in the resulting cyanide adducts. This novel method was successfully applied to the first imino‐Stetter reaction of aldimines obtained from 2‐aminocinnamic acid derivatives and aromatic aldehydes with cyanide, affording 2‐aryl‐substituted indole‐3‐acetic acid derivatives. Furthermore, the usefulness of this method was successfully demonstrated by the synthesis of an FPTase inhibitor, one of the biologically important 2‐arylindole‐3‐acetic acid derivatives.
By applying carbonyl compounds as sources of alkyl groups to the indium‐catalyzed reductive alkylation of indoles, a reliable and practical method capable of offering a wide range of alkylindoles with structural diversity has been developed. An important feature of this method is that the loading of the indium catalyst can be reduced by more than that of the original alkyne‐based system.
A straightforward method based on an iron(III) complex‐catalyzed cyclization of 2‐(1‐hydroxyallyl)phenols is reported to access a large variety of 2H‐chromenes. This method was applied to the total synthesis of a natural product, tephrowatsin B.
